Seaside volcano spouts fire and ice

THE cloud of gas and debris that erupted from the Rabaul volcano in Papua New Guinea in September 1994 contained at least two million tonnes of ice, according to American satellite observations.

This surprising discovery could explain why some volcanic clouds contain much less sulphur dioxide than might be expected. If a volcano ejects vast quantities of water which freezes in the upper atmosphere, some of this may combine with sulphur dioxide to form droplets of sulphuric acid that quickly rain back to Earth.

William Rose and his colleagues at Michigan Technological University in Houghton examined the Rabaul cloud using a radiometer on the US NOAA-12 satellite. They were initially puzzled by unusual signals recorded in two infrared bands which were absent from a dozen other eruptions. But later analysis showed that these signals were caused by spheres of ice between 18 and 80 micrometres across. There must have been ...

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